Since you mention two nocks, I will hazard a guess that you are gripping the string 3 under. Short bows can exaggerate the tiller problems from shooting a bow 3 under that was tillered for split fingers. This can result in the limbs being out of time with each other such that they don't return to brace height at the same time, which might result in porpoising. You might try holding the string 2 under, if the bow is light enough that you can do that without discomfort. This might balance the pull between the limbs better, or at least make it closer to a split finger pull. Some people pull with the index and middle fingers under, while others pull with the middle and ring fingers under, and just keep the index finger off the string by pointing with it, I think.
Another possibility is that you could correct the tiller by building up the rest higher, rather than raising the nock point. That worked on one of my bows one time where I couldn't get rid of nock high any other way.